Good question. Although I am not sure why that number was chosen, it was originally made to give people a hint or clue but to look like an address. For example, 1174 Lake Jackson 8pm. That way others won't know, but you would know the "secret message." It's similar to 420 being the code for marijuana. Hope that helps! I love teaching slang and expressions, so if you ever need more help, please let me know.